In recent years, a landscape TV screen is becoming popular due to diffusion of so-called high definition and wide vision TVs. However, on the other hand, in consideration of Japanese housing circumstances, a TV set which is narrow in width and thin as a whole is desired. As above described, although a TV screen is becoming long horizontally, the TV set which is narrow in width and thin as a whole TV is still desired, and thus a speaker unit (herein after referred to as speaker) to be mounted in the TV is required to be small and thin. Therefore, a speaker, which uses a copper foil pattern formed on a diaphragm as a voice coil, has been proposed (see, e.g. Patent Document 1).
Hereinafter, referring to FIG. 21, a conventional speaker will be described. FIG. 21 is a cross sectional view of the conventional speaker. The conventional speaker comprises a yoke 91, a magnet 92, a diaphragm 93, and a voice coil 94. The magnet 92 has a lower surface firmly fixed to a central portion of the yoke 91. In a space between the magnet 92 and the yoke 91, a magnetic gap 95 is formed. The diaphragm 93 is planate, and an extremity thereof is firmly fixed to the yoke 91. A central portion of the diaphragm 93 is firmly fixed to an upper surface of the magnet 92. The voice coil 94 comprises a copper foil pattern formed on an upper surface of the diaphragm 93, and is located on a whole surface of a part of the diaphragm 93, which is situated in the magnetic gap 95 (herein after referred to as vibrating portion).
Here, in the voice coil, a driving force is generated, in a vertical direction, by a motive current and magnetic flux within the magnetic gap 95. With the driving force, a vibrating portion of the diaphragm 93 vibrates vertically, and a sound is produced. In this way, the conventional speaker realizes downsizing with the copper foil pattern, which is formed on the upper surface of the diaphragm 93, used as the voice coil 94. Patent Document 1: Japanese Laid-Open Patent Publication No. 2001-211497